The challenge to meet the ever increasing demand for oil includes increasing crude oil recovery from heavy oil reservoirs. This challenge has resulted in expanding efforts to develop alternative cost efficient oil recovery processes (Kianipey, S. A. and Donaldson, E. C. 61st Annual Technical Conference and Exhibition, New Orleans, La., USA, Oct. 5-8, 1986). Heavy hydrocarbons in the form of petroleum deposits and oil reservoirs are distributed worldwide. These oil reservoirs are measured in the hundreds of billions of recoverable barrels. Because heavy crude oil has a relatively high viscosity, it is essentially immobile and cannot be easily recovered by conventional primary and secondary means.
Microbial Enhanced Oil Recovery (MEOR) is a methodology for increasing oil recovery by the action of microorganisms (Brown, L. R., et al., SPE 59306, SPE/DOE Improved Oil Recovery Symposium, Oklahoma, Apr. 3-5, 2000). MEOR research and development is an ongoing effort directed at discovering techniques to use microorganisms to modify crude oil properties to benefit oil recovery (Sunde. E., et al., SPE 24204, SPE/DOE 8th Symposium on enhanced Oil Recovery, Tulsa, Okla., USA, Apr. 22-24, 1992).
In MEOR processes, useful microbes are typically hydrocarbon-utilizing, non-pathogenic microorganisms, which use hydrocarbons as their energy source to grow or excrete natural bio-products such as alcohols, gases, acids, surfactants and polymers. These bio-products change the physio/chemical properties of the crude oil and stimulate changes in the oil-water-rock interactions to improve oil recovery.
The positive effects of the MEOR technology in a reservoir include: 1) altering the permeability of the subterranean formation to improve water sweep efficiency; (2) producing biosurfactants to decrease surface and interfacial tensions; (3) mediating changes in wettability; (4) producing polymers which facilitate mobility of petroleum; and (5) generating gases (predominantly CO2), increasing formation pressure and reducing oil viscosity thus promoting and re-establishing the gas drive in the reservoir. The combined effects of these bio-products decrease the capillary forces acting between the oil, the water and the rock, releasing the trapped oil.
Methods for identifying microorganisms useful in MEOR processes previously described require identification of the consortium of microorganisms in the samples drawn from an oil well or the sample under specific conditions with a defined nutrient medium in the presence of anaerobic gas mixtures (U.S. Patent Application No. 200710092930A1). A process for stimulating the in situ activity of a microbial consortium to produce methane for oil was described in U.S. Pat. No. 6,543,535B2. Such processes are time consuming and labor-intensive. Thus, there is a need for developing methods to: 1) develop a steady state population of consortium of microorganisms that can grow in or on oil under anaerobic denitrifying conditions; 2) identify the members of the steady state consortium for properties that might be useful in oil modification and/or interactions and 3) use said steady state consortium of microorganisms, in a cost-effective way, to improve oil recovery under anaerobic conditions.